div inside if statement javascript

Your code seems to work fine. I don't see the input container included in the code snippet you provided. Perhaps you need to make sure the id is correct there? I cleaned up the code a bit:

var div, div2, rightAnswer, problemNum = Math.floor((Math.random() * 3) + 1);
if (problemNum === 1) {
    rightAnswer = 14;
    div = document.getElementById("answerDisplay");
    div.textContent = "4 + 2 * (10 - 3 * 2) / 4 + 8 = ?";
} else if (problemNum === 2) {
    rightAnswer = 8;
    div = document.getElementById("answerDisplay");
    div.textContent = "(6 - 3) * 2 + (3^2 - 5) / 2 = ?";
} else if (problemNum === 3) {
    rightAnswer = 6;
    div = document.getElementById("answerDisplay");
    div.textContent = "5 - 3 + 4^2 / (8 - 4 / 2) = ?";
} else if (problemNum === 4) {
    rightAnswer = 3;
    div = document.getElementById("answerDisplay");
    div.textContent = "5^2 - (6 * 2) * 2 * (5 - 2) = ?";
}

function checkRightAnswer() {
    var answer = document.getElementById('Input').value;
    if (problemNum === 1 && answer === 14) {
        div2 = document.getElementById("correctOrNot");
        div2.textContent = "Correct";
        problemNum = Math.floor((Math.random() * 3) + 1);
    } else if (problemNum === 2 && answer === 8) {
        div2 = document.getElementById("correctOrNot");
        div2.textContent = "Correct";
        problemNum = Math.floor((Math.random() * 3) + 1);
    } else if (problemNum === 3 && answer === 6) {
        div2 = document.getElementById("correctOrNot");
        div2.textContent = "Correct";
        problemNum = Math.floor((Math.random() * 3) + 1);
    } else if (problemNum === 4 && answer === 3) {
        div2 = document.getElementById("correctOrNot");
        div2.textContent = "Correct";
        problemNum = Math.floor((Math.random() * 3) + 1);
    } else {
        div2 = document.getElementById("correctOrNot");
        div2.textContent = "Incorrect, try again";
    }
}

<div id="answerDisplay"></div>
<div id="correctOrNot"></div>
<input type="text" id="Input" />

Here is a way you would rewrite it to use an array of objects as ErikE suggested in his comment.

var questions = [
    {
      q: "4 + 2 * (10 - 3 * 2) / 4 + 8 = ?",
      a: 14
    },
    {
      q: "(6 - 3) * 2 + (3^2 - 5) / 2 = ?",
      a: 8
    },
    {
      q: "5 - 3 + 4^2 / (8 - 4 / 2) = ?",
      a: 6
    },
    {
      q: "5^2 - (6 * 2) * 2 * (5 - 2) = ?",
      a: 3
    }
  ],
  currentQuestion, // the index of the current question will
                   // be stored here so we can look up the answer later
  timerId,
  doc = document,
  elQuestion = doc.getElementById('question')
  elAnswer = doc.getElementById('answer'),
  elUserAnswer = doc.getElementById('user-answer'),
  elCheck = doc.getElementById('check'),

  displayQuestion = function (index) {
    currentQuestion = index;
    elQuestion.textContent = questions[index].q;
  },
  displayRandomQuestion = function () {
    displayQuestion(Math.floor(Math.random() * questions.length));
  },
  removeAnswer = function () {
    timerId = setTimeout(function () {
      elAnswer.textContent = ''
    }, 1000);
  },
  checkAnswer = function () {
    var userAnswer = elUserAnswer.value;

    clearTimeout(timerId);

    // the '' + explicitly converts the .a to a string because userAnswer will be a string
    // using the strict comparison operator (===) is a good habit to get into
    if (userAnswer === '' + questions[currentQuestion].a) { 
      elAnswer.textContent = 'Correct!';
      displayRandomQuestion();
    } else {
      elAnswer.textContent = 'Incorrect, try again';
    }
    removeAnswer();
  };

elCheck.addEventListener('click', checkAnswer, false);
displayRandomQuestion();

Working jsfiddle

Doing it this way is shorter, cleaner and easier to maintain as well. Adding a new question/answer pair is as easy as adding another object to the array. No more copy/pasting if statements and other redundant code. In addition since there is only one place where each action is performed (questions/answers are displayed, the answer is checked, etc) if there is a bug with any of these features there is a single well defined place to look for the bug and you only have to fix it once instead of once for every question in your quiz.

The way I have abstracted lots of the work also makes it easier to extend the code in the future. For instance if you further abstract out the random number code:

getRandomIndex = function () {
  return Math.floor(Math.random() * questions.length);
},

You can alter displayRandomQuestion so it will never repeat the same question twice in a row:

  displayRandomQuestion = function () {
    var index;
    do {
      index = getRandomIndex();
    } while (index === currentIndex);
    displayQuestion(index);
  },

Or even ensure questions never repeat until all the questions have been asked:

  askedIndexes = [],
  displayRandomQuestion = function () {
    var index;
    do {
      index = getRandomIndex();
    } while (askedIndexes.indexOf(index) !== -1);
    if (askedIndexes.length === questions.length - 1) {
      askedIndexes = [];
    }
    askedIndexes.push(index);
    displayQuestion(index);
  },